The object of these studies is to explore mesenteric hemodynamic responses to interventions which evoke ischemia and to agents which will dilate the constricted intestinal circulation. Interventions include endotoxin, oligemia and cardiac glycosides. Dilator agents include prostaglandin E1, histamine, glucagon, isoproterenol and the calcium channel blocker perhexyline. Measurements to be made include systemic arterial and portal venous pressures, superior mesenteric artery blood flow, systemic arterial and mesenteric venous oxygen content, intestinal wall distribution of radiolabelled microspheres, 86Rb clearance by the mesenteric circulation.